This invention relates to an apparatus and a method of testing an anti-lock brake system or anti-wheel-lock brake system under a condition that wheels of a vehicle such as a motorcar are placed on rolls.
As this kind of apparatus, there is known in Japanese Published Unexamined Patent Application No. 233349/1988 an apparatus in which each of rolls for mounting thereon each of the wheels of the vehicle is made up of a pair of front and rear split rolls to be rotated in interlocking with each other. The friction coefficient of the rear split rolls is made small so that, when the centers of the wheels are offset rearwards at the time of braking due to the relationship between the braking force of the wheels and the rotational force of the rolls, a slip is caused to occur between the rear split rolls and the wheels. The wheels are thus brought into a locked condition so that a reduction in the braking pressure by anti-lock control is performed. When the centers of wheels are moved forwards due to the lowering in the braking force as a consequence of this pressure reduction, the wheels are accelerated by the front split rolls and the braking pressure is increased. By this increase in the braking pressure, the wheels are again offset backwards to cause a slip relative to the rear split rolls, whereby the increase and reduction in the braking pressure are repeated.
According to the above-mentioned conventional apparatus, the increase and reduction in the braking pressure by the anti-lock control is realized in the same manner as if the vehicle were actually running on the road, and the operating conditions of the anti-lock brake system can be judged from the changes in the rotational speed of the wheels. However, in this apparatus, since the wheels slip relative to the rolls, the rotational speeds of the wheels do not coincide with those of the rolls. Therefore, in order to detect the rotational speeds of the wheels, it is necessary either to pick up signals from wheel speed sensors which are mounted in advance on the vehicle for the purpose of controlling the anti-lock brake system or to separately mount sensors on the vehicle. This results in troublesome preparation works.
As can be seen in Japanese Published Unexamined Patent Application No. 99879/1979, the anti-lock brake system performs the following control. When the deceleration of the wheels has exceeded a standard deceleration, the increase in the braking pressure is stopped. At the same time, that standard speed at the time of braking which is determined on the basis of a pseudo-speed of the vehicle to be calculated by the rotational speed of each wheel, is compared with the wheel speed. When the wheel speed is below the standard speed at that instant, the braking pressure is reduced until the deceleration lowers to or approaches the standard deceleration. As soon as the wheel speed has exceeded the standard speed at that instant, the braking pressure is increased.
Accordingly, even if the wheels are not caused to slip on the rolls, the anti-lock brake system is operated if the inertia weight of the rolls is made small so that the deceleration of the wheels at the time of braking increases above a predetermined level. In this case, when the inertia weight of the rolls is too small, the wheels come to a stop before the braking pressure is actually reduced, due to the delay in response for increasing or reducing the braking pressure.